The present invention generally relates to a fuel intake system in an automobile internal combustion engine and, more particularly, to an improved fuel intake system for automatically controlling the temperature of an incoming air to be introduced into one or more engine cylinders together with fuel.
In order to improve, or stabilize, the combustion condition in the engine cylinders, some automobiles have employed a heated fuel intake system so designed as to heat the incoming air when the temperature of the latter is lower than a predetermined operating temperature, the heating of the incoming air being interrupted when the temperature of the incoming air so heated subsequently becomes higher than the predetermined operating temperature. In this prior art system, the predetermined operating temperature at which the heating system operates is generally within the range of 30.degree. to 50.degree. C. and is determined in consideration of the incompatible facts that evaporation and/or atomization of fuel to be mixed with the incoming air to provide a combustible air-fuel mixture can be facilitated when the temperature of the incoming air is relatively high and that the charge efficiency for the engine cylinders can be improved when the temperature of the incoming air is relatively low.
The prior art heated fuel intake system of the type referred to above is effective only when used under the circumstances where the ambient temperature, which may be the temperature either inside or outside the automobile engine compartment, is lower than the predetermined operating temperature. Conversely, when the prior art heated fuel intake system is used under the circumstances where the ambient temperature higher than the predetermined operating temperature prolonges substantially, the temperature of the incoming air is correspondingly high, rendering the heating system unable to maintain the temperature of the incoming air at a constant value corresponding to the predetermined operating temperature.
In addition, since the mixing ratio of the air-fuel mixture to be supplied into the engine cylinders is generally set to the stoichiometric value which is determined by taking the predetermined operating temperature into consideration as one of the determinant factors, the increased temperature of the incoming air higher than the predetermined operating temperature would reduce the mixing ratio, that is, enrich the air-fuel mixture, to such an extent that satisfactory combustion of the air-fuel mixture will no longer take place in the engine cylinders, thereby adversely affecting the drivability of the automobile paralleled with the substantially increased amount of noxious unburned components of the exhaust gases. The higher the ambient temperature, the more often is this occurrence enhanced.
In order to avoid the drawbacks inherent in the prior art heated fuel intake system of the type referred to above, the U.S. Pat. No. 4,112,896, patented on Sept. 12, 1978, discloses a heated fuel intake system which comprises a thermostatic valve for introducing warmed air into the engine and air to a slow-port passage of a carburetor. The thermostatic valve comprises a valve casing defining therein first and second compartment. The first compartment has a first valve member for controlling the introduction of the intake vacuum or the atmospheric pressure to a negative pressure motor mounted on a throat or snorkel tube of an air cleaner. The second compartment has a second valve member for controlling the communication between a float chamber and the slow-port passage of the carburetor when the temperature of the air introduced into the engine exceeds a preset value so as to prevent excessive richness of an air-fuel mixture flowing towards the engine.
In the system disclosed in the above mentioned U.S. patent, since the air is introduced into the slow-port passage when the air inside the air cleaner exceeds the preset value, it involves a such a problem that, because the adjusted air-fuel ratio merely corresponds to a value appropriate for the engine to operate with the air heated to such preset temperature, the combustible air-fuel mixture tends to be enriched or leaned once one or both of the temperature of the air so introduced and the ambient temperature diverge from the preset temperature.